News: The Supreme Court has asked the RO Manufacturers Association to approach the government on the National Green Tribunal’s order prohibiting the use of reverse osmosis (RO) purifiers where total dissolved solids (TDS) in water are below 500 mg per litre.
Background: The NGT in its order on May 20 had directed the Ministry of Environment, Forests and Climate Change to frame rules for manufacturing and sale of RO filters, and banned use of RO in areas where the Total Dissolved Solids (TDS) in water was already low.
- Osmosis is a phenomenon where water/ solvent flows from a dilute (less concentrated) solution through a semi permeable membrane to a higher concentrated solution.
- Semi permeable means that the membrane will allow small molecules and ions to pass through it but acts as a barrier to larger molecules or dissolved substances.
- Osmosis is a special case of diffusion. Diffusion is the movement of molecules from a region of higher concentration to a region of lower concentration
- Reverse osmosis occurs when water moves through a semi-permeable membrane in the direction opposite to that for natural osmosis. This happens when the water is pushed under greater pressure than the osmotic pressure.
- Boiler feed-water treatment: used to reduce solids content of waters prior to feeding into boilers for power generation or otherwise.
- Desalinization: It is widely used to desalinate the sea water.
- Used in wastewater industries and in many commercial industries to purify the water to get safe drinking water.
- Used in beverage industry for concentrating the food liquids such as fruit juices.
Total dissolved solids (TDS):
- It is the term used to describe the inorganic salts and small amounts of organic matter present in solution in water.
- The principal constituents are usually calcium, magnesium, sodium, and potassium cations and carbonate, hydrogencarbonate, chloride, sulfate, and nitrate anions.
- According to the Bureau of Indian Standards (BIS), the upper limit of TDS level in water is 500 ppm. The TDS level recommended by WHO is 300 ppm.